Radio Frequency (RF) shielding may be required on certain semiconductor devices and modules (hereinafter semiconductor device) in order to minimize Electro-Magnetic Interference (EMI) radiation from the semiconductor device. RF shielding is further required to prevent RF radiation from external sources from interfering with operation of the semiconductor device
RF shielding is generally accomplished in one of three ways. A first method is to attach a metal can over the component after the component is attached to the motherboard. An alternative to the shield attached method is an embedded RF shield. In an embedded shield, the metal RF shield is directly attached to the semiconductor package substrate by means of solder or a conductive adhesive. The shield may be fully embedded within the mold compound of the finished package or can be exposed after assembly. The third method is the conventional conformal shield. In this method, all of the components are placed on the substrate and the substrate, or strip, is over-molded using unit molding, or pin gate molding where individual mold caps are defined within the strip such that upward facing, exposed pads in the substrate remain exposed after the mold operation. A conductive coating is then applied to the strip such that it covers the units and also makes electrical contact to the upward facing pads. The strip is then singulated into individual units.
RF shielding is strongly impacted by the electrical resistance of the RF shield to ground. This resistance is comprised of the resistance of the RF shield, connection of the RF shield to ground, know as contact resistance, and trace resistance. The contact resistance is generally dictated by the amount of corrosion and or oxidation that may form on the exposed metal traces and or ground planes prior to connection of the RF shield to the exposed metal traces and or ground planes.
Therefore, a need existed to provide a system and method to overcome the above problem. The system and method would lower the electrical resistance of the RF shield to ground by lowering the contact resistance.